add singleton meta with no args

app/utils/singleton.py

@@ -16,3 +16,21 @@ class SingletonMeta(type):
                 instance = super().__call__(*args, **kwargs)
                 cls._instances[cls] = instance
         return cls._instances[cls]
+
+
+class SingletonMetaNoArgs(type):
+    """
+    Singleton metaclass for classes without parameters on constructor,
+    for compatibility with FastApi Depends() function.
+    """
+
+    _instances = {}
+
+    _lock: Lock = Lock()
+
+    def __call__(cls):
+        with cls._lock:
+            if cls not in cls._instances:
+                instance = super().__call__()
+                cls._instances[cls] = instance
+        return cls._instances[cls]